Ember Data multiple polymorphic relationships on the same model

I'm trying to get multiple polymorphic relationships going on the same model. Previously I had just one, and that worked just fine. I extended the polymorphic class and it works.

See example: http://ift.tt/1K8jKrf

I have double extended my classes to get the second polymorphic relationship to work.

See example: http://ift.tt/1zExh6N But I am not comfortable with that. As it doesn't represent what is happening with the data accurately. Yes they are related in a way, but by no means do they depend on each other like that.

Doing some research some have suggested doing mixins. http://ift.tt/1K8jJ6F And it has apparently been pulled into Ember Data http://ift.tt/1zExirC But I just can't get it to work.

Anyone have a suggestion on how to do this with my jsbin?

Thanks!